Miss Fortune has significantly higher range aside from Grave's ultimate. Not only that but Miss Fortune's poke is on a lower cooldown, does more damage, has higher range, and also has a lower mana cost, the damage is significantly stronger if you land the execute-double-up too.
The difference between Graves and Miss Fortune is that Miss Fortune can poke more effectively and her range also lets her do much better against someone like Caitlyn, Varus, or Ashe who have higher ranges due to their base auto attack range or their abilities. However, Graves can definitely all in better than Miss Fortune.
They actually are pretty similar, I'd probably say pick Miss Fortune if you want to destroy the laning phase or counter a lane bully like Caitlyn and have a good teamfighter, and pick Graves if you have someone who can all in well like Leona but also he has a better late game than Miss Fortune.
In terms of damage which both Graves and Miss Fortune are pretty much designed to do in comparison to someone like Sivir who has more utility, or Ashe who has more CC, Miss Fortune would easily win sustained fights since her ultimate can do much damage than Graves' ultimate given the time, and her W passive allows her to win pretty much any sustained fight against ADCs if it does continue long enough. Graves would probably be better for burst though.
Overall Graves and Miss Fortune (or Lucian) aren't "better" or "worse" than each other, they're different ADCs and do things better and worse than each other, but definitely aren't just clearly superior in every way. Miss Fortune is better poke, Graves is better all in, Lucian is better mobility, all teamfight pretty well.